# Designing Metrics

Cube is a dataset-centric semantic layer, where all primary objects, cubes and views, are table-like datasets.
When designing how your semantic layer will be exposed and consumed by end users, you can follow either entity-first approach or metrics-first. 
In both cases, views will be used to build the semantic layer interface. 

## Entity-first

In entity-first approach, views are built around entities in your data model. 
Views are built as denormalzied tables, bringing measures and dimensions from different cubes needed to fully decscribe the entity.

```yaml
views:
  - name: orders_view

    cubes:
      - join_path: orders
        includes:
          - status
          - created_at

          - completed_count
          - count
          - total_amount
          - average_order_value

      - join_path: orders.users
        prefix: true
        includes: 
          - city
          - age
          - gender
```

In our example ecom project, these would be `orders` or `line_items`. 
In the example below we define `orders_view` view to describe `orders` entity. It has multiple measures and dimensions

You can optionally create multiple views to describe single entity. 
It can be useful for entities with a large number of dimensions to not overwhelm the end users with all the possible dimensions in a single view, 
but instead creating multiple slices of data with only relevant measures and dimensions.

In the example below, we are breaking down `orders_view` into `orders_view` and `orders_with_users_view`. 
Only the latter view will contain dimensions related to user who placed the order.

```yaml
views:
  - name: orders_view

    cubes:
      - join_path: orders
        includes:
          - status
          - created_at

          - completed_count
          - count
          - total_amount
          - average_order_value
```

```yaml
views:
  - name: orders_with_users_view

    cubes:
      - join_path: orders
        includes:
          - status
          - created_at

          - completed_count
          - count
          - total_amount
          - average_order_value

      - join_path: orders.users
        prefix: true
        includes: 
          - city
          - age
          - gender
```
Views are exposed as tables in Cube SQL API, dimensions can be queried as is 


## Metrics-first
In metrics-first approach, views are built around measures, or metrics, in your data model.
Views are built as denormalzied tables, containing one measure and all the relevant dimensions from different cubes. These include all the dimensions you would group or filter by, and up to one time dimension.  
Views are usually named after that single measure.

```yaml
views:
  - name: average_order_value

    cubes:
      - join_path: orders
        includes:
          - average_order_value

          - status
          - created_at

      - join_path: orders.users
        prefix: true
        includes: 
          - city
          - age
          - gender
```


```sql
SELECT
  status,
  MEASURE(average_order_value)
FROM average_order_value
GROUP BY 1
```

NOTE: If a metric is interesting across more than one time dimension, create multiple views (metrics), one with each time dimension, and name the metric distinctly for each.  
This approach improves compatibility with BI tooling and adds clarity for the consumer.

```yaml
views:
  - name: order_count_by_order_date

    cubes:
      - join_path: orders
        includes:
          - order_count

          - status
          - created_at

  - name: order_count_by_ship_date

    cubes:
      - join_path: orders
        includes:
          - order_count

          - status
          - shipped_at
```

## Integrations with BI Tools
Some metrics-based BI tools will specify requirements for the views or be able to accept additional metadata to enrich the experience.  
Below is an example of using the `meta` property to do this.

```yaml
views:
  - name: order_count_by_order_date
    description: For finance team to track orders on accrual/earned basis.
    meta:
      type: metric
      owner: alice@acme.com

    cubes:
      - join_path: orders
        includes:
          # MEASURE
          - order_count

          # TIME
          - created_at

          # DIMENSIONS
          - status
          - city
```
